Compositions which are crosslinked by irradiation have been disclosed heretofore for preparing coatings which repel tacky substances. Hockemeyer, for example, describes in U.S. Pat. No. 4,571,349, organopolysiloxane compositions which are crosslinked by high energy radiation to form coatings consisting of siloxane units of the formulas:
(a) HR.sup.1 C.dbd.CR.sup.2 COOR.sup.3 SiR.sub.2 O.sub.1/2 ; PA1 (b) HSR.sup.4 SiRO; and PA1 (c) R.sub.2.sup.5 SiO,
where R is a monovalent hydrocarbon radical or a halogenated monovalent hydrocarbon radical, R.sup.1 is hydrogen or a phenyl radical or a halogenated phenyl radical, R.sup.2 is hydrogen or an alkyl radical having from 1 to 4 carbon atoms, R.sup.3 is a hydrocarbon radical or a halogenated hydrocarbon radical, R.sup.4 is a divalent hydrocarbon radical, R.sup.5 is the same as R or a hydrocarbon radical substituted with the HR.sup.1 C.dbd.CR.sup.2 COO group, where R.sup.1 and R.sup.2 are the same as above, in which two siloxane units of the formula HR.sup.1 C.dbd.CR.sup.2 COOR.sup.3 SiR.sup.2 O.sub.1/2 are present per molecule.
U.S. Pat. No. 4,064,027 to Gant describes a composition which is curable upon exposure to ultraviolet light consisting of a siloxane consisting of (A) vinyl-containing siloxane units of the formula ##EQU1## where R is a monovalent hydrocarbon radical or a halogenated monovalent hydrocarbon radical and n has a value from 0 to 2, (B) a siloxane containing at least one silicon-bonded hydrogen atom, and (C) a cure accelerator having the formula ##EQU2## where R"' is a divalent or trivalent hydrocarbon radical, one bond of which is attached to the silicon atom and the other bonds are attached to the mercapto groups, p has a value of 1 when R"' is divalent and a value of 2 when R"' is trivalent, q has a value of 1 or 2, R"" is a monovalent hydrocarbon radical, v is from 0 to 2 and the sum of q and v is from 1 to 3, L any other siloxane units present in (C) having the general formula ##EQU3## where Q is a monovalent or halogenated monovalent hydrocarbon radical and t has a value of from 0 to 3.
Even though organopolysiloxanes containing units of the formulas EQU R.sub.3.sup.6 SiO.sub.1/2 and EQU R.sup.6 SiO.sub.3/2,
where R.sup.6 is a radical of the formula HSR.sup.4 --, or a monovalent or halogenated monovalent hydrocarbon radical or a hydrocarbon substituted by a group of the formula HR.sup.1 C.dbd.CR.sup.2 COO, where R.sup.1 is hydrogen or a halogenated phenyl radical, R.sup.2 is hydrogen or an alkyl radical having from 1 to 4 carbon atoms per radical and R.sup.4 is a divalent hydrocarbon radical, are described in the patent to Gant, it does not disclose organopolysiloxanes containing units of the formulas EQU HR.sup.1 C.dbd.CR.sup.2 COOR.sup.3 R.sub.2 SiO.sub.1/2, EQU HSR.sup.4 SiRO and EQU R.sub.2.sup.5 SiO,
where R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are the same as above.
Moreover, Gant does not disclose that compositions containing organopolysiloxanes made from units of the formulas EQU R.sub.3.sup.6 SiO.sub.1/2 and R.sup.6 SiO.sub.3/2,
where R.sup.6 is the same as above, can increase the separation value.
It is an object of the present invention to provide compositions which are crosslinked when exposed to a radiation source. Another object of the present invention is to provide compositions which crosslink rapidly upon exposure to a radiation source. Another object of the present invention is to provide compositions which can be crosslinked to form coatings which have adhesive-repellent properties. Still another object of the present invention is to provide coatings having an increased separation value. Still another object of the present invention is to provide coatings in which the improved separation value remains constant even after storage. A further object of the present invention is to provide coatings having predetermined separation values that remain substantially constant. A still further object of the present invention is to provide compositions which are substantially free of unpleasant odors.